Crutch-tip.



P. W. PRATT.

GRUTGH TIP.

APPLIOATION FILED APR. 3. 1909.

rammed June 7,1910.

M ATTYE.

w m W P W Du u M P v To all whom it may concern:

UNITED STATES 1 PATENT orrron.

PHILIP W. PRATT, 0F BOSTON, MASSACHUSETTS.

CBUTCH-TIP.

Specification of Letters Patent.

Patented June 7, I910.

Application filed April 3, 1909. Serial No. 487,795.

Be it known that I, PHILIP W. PRA'I'I, of

Boston, in the county of Suffolk and State of Massachusetts, haveinvented certain new and useful Improvements in Crutch-Tips, of whichthe following is a specification.

The present invention relates to sockettips of rubber adapted to heslipped upon the ends of crutches toprovide a: cushion therefor anddiminish the liability of slip.-

ping.

It consists in a wear plate or washer of metal which is so shaped as totransmit the pressure of the crutch, due to the weight of the user, tothe circumference of the tread s\ 1rface of the tip so that the wearwill be distributed over the tread surface more generally than hasheretofore been the case, instead of being localized at the center ofthe tread. Heretofore, where crutch tips without metal plates have beenapplied di rectly to the ends of crutches or where a metal plate, fiaton its under surface, has been inserted to diminish wear, the pressureof the crutch has been more or less concen-' trated upon the center ofthe tread of the tip with the result that a hole has been quickly wornthrough while the outside or periphery of the tread has been hardly wornat a construction and arrangement that the pressure may be transmitteddirectly to the outer edges of the bearing surface under all conditionsof use and regardless of the direction in which the crutch staff mayextend with respect to the ground or floor.

In the accompanying drawings, Figure 1 represents a sectional view of asocket crutch tip having a wear plate or washer embodying the featuresof my invention inserted therein. Fig. 2 represents a similar view of asomewhat different type of socket tip in which the bottom of the socketis a central cavity 0 surrounded by a depressed annular bearing zone (Zwhich bears against the bottom of the socket in the tip. The edges 6 ofthe plate are turned up slightly so as to avoid liability of cuttinginto therubber ofwhich the tip is made.

As shown in Fig.1, the crutch tip 6 has formed on the bottom of theinternal socket upstanding concentric integral ribs f of rubber whichare adapted to .yield more than a solid'body of rubber would do, so

as to give a cushioning effect. In Fig. 2 the bottom of the socket isplain and the cushioning effect is given by a Washer of felt or similaryielding material whic ,is'

inserted under the metal washer orv plate a.

Preferably the metal plate has on its upper surface a convexity or crownh which is I located at the centerand receives directlfly the pressureof the" end of the, crutch sta The preferred manner of making the washeris to cut the circular disks from comparatively thin sheet metal andsubject" the disks to pressure between suitabie dies shaped so as topress up the center in ed es and to press down the intermediate annu arzone. This, of course, is not the only way in which the washers could beformed but is preferable on account of being the quick:

est and cheapest. It 1s therefore the 0b ect of my lnvention to providea washer or wear-plate of such On account of the fact that the washerthe periphery of the tread surface, while the central part is raisedabove the bottom of the tip, the pressure transmitted when any weight isapplied to the crutch acts principally upon the periphery of the tread.This is due to the fact that the concavity allows the central part ofthe tip bottom to rise and to press slightly upon the ground while theheavy pressure is borne by the edges of the tread. The concavity alsoallows a stretching or flowing of the rubber toward the center wherebyreater resilience and a greater cushioning e ect in the tip is given.These effects are intensified by the fact that the upper edge of theplate is convex above the concavity so that the crutch staff bears onlyon the center of ;bears upon the bottom of the crutch tip only. 1 on anannular surface substantially above let the plate. Thereby, whatever theinclination of the crutch may be when the tip strikes the ground, thepressure will be transmitted to the edges of the tread. I desire it tobe understood, however, that the concavity in theunder surface of theplate the side of the tip,

is =mainly instrumental in producing this effect, and that. the platewhich is flat on its upper surface but having the cavity underneath.would also produce similar results. The concavity allows the bottom ofthe tip to shape itself to the form of the plate and thereby vieldcentrally, equalizing the wear over the entire tread surface. Theconvexity on the upper surface of the plate allows a certain amount ofoscillation of the tip bottom in any direction so as to give anapproximately even bearing on the ground when the crutch staff is"inclined and thereby increase the wear and diminish the tendency toslip. It also allows the tip to be more easily turned when the wear becomes greater on one side than on the others.

From the above description it will be seen that the essential feature isthat the plate It, whatever its method of manufacture, provides fornormally maintaining or formmg a space at the center of that portion ofthe tip which receives the pressure of the crutch staff. By normally Imean that under some pressures the bottom of the crutch tip may perhapsbe pressed up so as to close said space. 1 But when not sub jected toheavy pressure there is always a space at the center of the tip so thatsaid tip may yield centrally as hereinbefore mentioned.

In order to retain the upper rim of the socket against the sides of-thecrutch staff, I provide a spring holder consisting of a ring a andresilient fingers j. The ring 71 surrounds the crutch above the top ofthe tip and incloses the upper edge, thereof, while the fingers bear uon the outer surface of the tip a out mi -way between its upper end andthe tread surface. These fingersare yielding so as to permit of thepivotal action above describedof the crutch stafl' on the plate h, butat the same time, they prevent the ed eof the tip separating from thecrutch, and thus give greater firmness. The inwardly-turned flange It:also prevents matter workin the tip between the we s thereof and thecrutch. 4

The turned-up edges e of the plate a act g ard to revent the edges ofthe crutch stafi P caring and cutting into the rubber at The bodyportion of the crutch' tip is composed of vulcanized rubber having asuitable egree of elasticity, and the tread face is formed as hereshown, by inserting a plug in partially into the base of the bodyportion, said plug'being formed from a strip of textile fabric, such ascanvas, suitably treated on its sides with rubber cement and woundspirally to form a disk, the sides of which are formed by the edges ofthe convolutions of the strip, this form of plug to each other, and thethat shown 1n into the socket of being similar to that shown in theFoster Patent No. 695,298, -nted March 11, 1902. GM side of the plug isembedded in the rubber body before the latter is vulcanized, theconvolutions of the plug being secured p ug as a .whole secured to thebodyof the ti b vulcanization.- The plu here shown difi'ers from theFosterpatent in that its tread face is corrugated and provided withnumerous projections and recesses, as shown in Figs. 1 and 2, bsubjecting the plu to pressure of a suitab e corrugatmg die be ore thevulcanizing o era'tion. The die forms the depressions an projectionswhile the plug is in a soft condition, these being made per; manent bythe vulcanization of the plug. A plug. of textile fabric formed as shownin the Foster patent, presents a surface which is less liable to slip,than a rubber surface. l have found that by corrugating the base of theplug as described, its liability to slip is still further decreased; Bythe employment of a stri of textile fabric such as canvas, some of t ethreads or strands must be presented endwise at the bottom face of thelug. And when the plug is subjected to t e pressure of a die which willproduce the de ressions and rojectlons mentioned, such t reads or strans are more or less condensed lengthwise according to their positionsrelatively to the a exes of the projections; thatis, those threa 3 whoseends are at the bottoms of the recesses are more shortened and condensedthan those whose ends are at the apexes of the projections, while thoseWhose ends are at the inclined sides of the pro'ections are in anintermediate condition 0 'condensity. The sides ofthe rojections ofcourse face or incline in di erent directions and consequently resentthreads which are more or less con ensed andso that their ends are atsuch an les to the surfaces of the inclines as to alfor the best 0position to slipping on the surface on whic the lug bears. This isespecially useful when t e tip is new because a freshlymolded' tip andplug is more likel to sli than when worn.

W at if c aim is 1. The-combination with a crutch tip, of apressuresustaining member having a central concavity in its bottom faceto form a normal 0 en space at the center of that portion of the tipwhich receives the pressure of the crutch stad.

2. In combination with a crutch tip, a plate for sustaining the thrustof the crutch stafi', bearing on the bottom of the tip on a zone nearits circumference and separated therefrom in its central portion,whereby a washer ha a depressed annular ortion to bear on t e bottom ofthe tip so et, and a raised central portion, forming a cavity on itsunder side to permit yielding of the center ofthe tip, and a convexcrown on its upper side to take the thrust of the central staff.

4. A washer for socket crutch tips, having an indented or ofiset centerand a turned-up periphery, thereby providing in its under surfaceacentral cavity surrounded by an annular bea g zone, and on the face acentral convex crown.

5. In combination with a crutch, a socket upper sur- "crutch, and aholder consisting of a rin surrounding the edge of the tip, andresilient fingers bearing against the sides of the tip for holding thelatter adjacent the surface of the crutch.

In testimony whereof I have aflixed my signature, in presence of twowitnesses.

' PHILIP W. PRATT. Witnesses:

ARTHUR H. BROWN, P. W. Pnzzm'rl.

